RAID power safe apparatus, systems, and methods

ABSTRACT

Apparatus and systems, as well as methods and articles, may operate to sequence write operations and journal a portion of write data in a dual-parity redundant array of inexpensive disks (RAID) sub-system such that one or more parity strips in a stripe are consistent with target stripe data during the write operations, such that the consistency of the parity strips is determinant following an unexpected RAID sub-system reset occurring during the write operations, and such that the parity strips and the target stripe data are recoverable following a disk drive failure and a power failure occurring during the write operations.

TECHNICAL FIELD

Various embodiments described herein relate to digital mass storagegenerally, including apparatus, systems, and methods used to write to aredundant disk array.

BACKGROUND INFORMATION

A redundant array of inexpensive disks level six (RAID-6) sub-system mayutilize two redundancy strips, parity and Q, in a stripe to aid inreconstructing a RAID volume in case of a single or double disk drivefailure. A RAID controller operating to update a data strip in thestripe may be required to update parity and Q associated with the stripeto ensure that the data is doubly protected. If an unexpected reset(e.g., a reset caused by a power failure) intervenes while the write isin progress, it may be difficult to determine which updates have beencompleted. Thus parity and Q associated with the affected stripe mayboth require re-calculation at the next re-boot following the powerfailure. Data in the strip targeted by the write in progress may beindeterminate, since the write to the targeted strip may have beeninterrupted by the power failure. However, data on parallel strips inthe stripe may be unaffected by the power failure. If both the power anda disk drive fail during write operations, upon re-boot both parity andQ may be indeterminate. In the latter case, the entire volume may befailed since it may not be possible to rebuild the stripe correctly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus and a representative systemaccording to various embodiments of the invention.

FIG. 2 is a flow diagram illustrating several methods according tovarious embodiments of the invention.

FIG. 3 is a block diagram of an article according to various embodimentsof the invention.

DETAILED DESCRIPTION

FIG. 1 comprises a block diagram of an apparatus 100 and a system 180according to various embodiments of the invention. It should be notedthat some embodiments described herein may apply to RAID-6 sub-systems.The terms “first parity” and “second parity” used herein for generalitymay sometimes be referred to as “parity” and “Q” in a RAID-6 context.Some embodiments of the invention may operate to recover from anunexpected reset (e.g., caused by a power failure, an operating systemcrash, or component failure) and a single disk drive failure occurringwhile RAID writes are in progress. Recovery may proceed by determiningwhether parity, Q, or both are valid upon re-boot following theunexpected reset. For purposes described herein, “valid” means capableof being combined with other strips in a stripe to reconstruct a damagedor missing strip. The strip could be missing as a result of disk failureor unavailability, for example.

Some embodiments of the invention may make a record, sometimes referredto herein as a “dirty stripe journal,” of a stripe affected by a writein progress before the write is allowed to update parity, Q, or data ona target disk. The record may be saved to non-volatile memory, to disk,or to other non-volatile storage to be used to determine which stripesrequire parity and Q re-calculations upon re-boot. Some embodiments ofthe invention may operate to order data, parity and Q updates such thatparity, Q, or both are valid during write operations affecting anassociated data strip. Information about the write in progress may beadded to the dirty stripe journal such that the validity of parity and Qcan be determined upon re-boot following the unexpected reset.

In some embodiments of the invention, ordering may be enforced such thatparity is updated on a target disk 161 before a data update, and Q isupdated following the data update. As a result, both parity and Q may bevalid before the updates, Q may be valid following the parity update andbefore the data update, and parity but not Q may be valid following thedata update but before the Q update. Both parity and Q may again bevalid following the Q update.

Some embodiments of the invention may thus write a record valid forrecovery from a power failure occurring between a time of writing therecord and a time of completing target disk updates. Calculations todetermine parity and Q update values may require that pre-update data beread before overwriting a strip with update data. The pre-update dataand the update data may thus exist in memory simultaneously. Someembodiments may search the pre-update data and the update data for afirst data increment (e.g., a one-byte sample) that differs between thetwo. A note may be made in the dirty stripe journal to identify thissample either by its update data value or by its pre-update data valueand by its location as an offset from the start of the data strip.

For the sequence of write operations described above, an equalitybetween the journaled sample and the identified sample in the data stripmay indicate that parity is valid upon re-boot. Thus, parity may be usedto reconstruct both the data strip and the Q strip in the target stripe.Likewise, an inequality between these values may indicate that Q isvalid. In the latter case, Q may be used to reconstruct both the datastrip and the parity strip for the affected stripe. Some embodiments ofthe invention may reverse the sequence of writing parity and Q. That is,Q may be updated first, and then data may be updated followed by parity.In the latter case, an equality between the journaled sample and theidentified sample in the data strip may indicate that Q is valid uponre-boot. An inequality between the two values may indicate that parityis valid upon re-boot. A similar result may obtain if pre-update data isjournaled rather than update data, with the parity and Q equalitiesreversed.

An example method may journal update data and may assume both parity andQ to be valid prior to updates to a target stripe 114. First, the dirtystripe journal may be updated with the update data value. Since the datastrip contains pre-update data at this point, a comparison between thejournal and the data strip upon re-boot may indicate that Q is valid.(Note that both parity and Q may be valid at this point.) The examplemethod may next update parity. Now only Q may be valid. The examplemethod may next update the data strip. Since the data strip contains theupdate data, only parity may be valid. The example method may nextupdate Q. Since the journaled sample value is now equivalent to itscounterpart written to the data strip, the method may indicate parity tobe valid. (Note that both parity and Q may be valid at this point.) Theexample method may next clear the entry associated with the target datastrip from the dirty stripe journal. The method may indicate by thecleared status that no write is in progress on the affected stripe, andthat both parity and Q are thus valid. The dirty stripe journal may bewritten to a disk drive, to non-volatile random-access memory (NVRAM),or elsewhere to be used for later analysis following an unexpectedreset.

Data may be recovered during a re-boot following an unexpected reset ifa disk drive within the RAID sub-system is first detected as failedduring the re-boot. The journaled sample data and its expected locationon the data strip may be read from the dirty stripe journal followingthe re-boot. The sample data may also be read from the expected locationwithin the target data strip. The two versions of sample data may thenbe compared to determine whether parity or Q is valid, and which shouldbe used to reconstruct the other as well as the data strip. If thefailed disk is a parity or Q strip for the stripe, then the data stripmay still be intact. The stripe may thus have survived both the diskfailure and the unexpected reset. If the failed disk is the target datadisk, parity, Q, or both may be used to reconstruct the data strip. Someembodiments and methods disclosed herein may treat operations affectingmore than one data strip in a stripe as two separate writes, one to eachstrip. Some embodiments and methods may write a journal entry for each“atomic” portion of a data strip. That is, the journal entry may bewritten for a portion of a strip update specified by the target diskdrive characteristics to complete following the unexpected reset.

In some embodiments, the apparatus 100 may include logic 102 in a RAIDsub-system 112, including perhaps a dual-parity RAID sub-system. TheRAID sub-system 112 may be capable of sequencing write operations andjournaling a portion of write data such that one or more parity stripsin a target stripe are consistent with target stripe data during thewrite operations. Write operations and journaling may proceed such thatthe consistency of the parity strips is determinant following anunexpected RAID sub-system reset occurring during the write operations.The logic may enable the RAID sub-system 112 to recover the paritystrips and the target stripe data following a disk drive failure and apower failure occurring during the write operations.

The apparatus 100 may include a sequencing module 106 to establish anorder of operations associated with a disk drive update to a data strip110A, 110B in a RAID sub-system 112, including perhaps a RAID-6sub-system. The data strip 110A may be associated with the stripe 114,and may be updated with a data strip update value 118A, 118B. An updatemay also be made to a first parity strip 122 associated with the stripe114 using a first parity strip update value 126. Additionally, an updatemay be made to a second parity strip 130 associated with the stripe 114using a second parity strip update value 134. The sequencing module 106may order the update operations such that the update to the first paritystrip 122 is written before writing the update to the data strip 110A,and the update to the second parity strip 130 is written after writingthe update to the data strip 110A.

The apparatus 100 may also include a journaling module 138 coupled tothe sequencing module 106 to create a journal entry 142 in anon-volatile storage medium 146 before writing the update to the firstparity strip 122. The journal entry 142 may comprise first identifyingdata 150A, 150B within the data strip update value 118A, 118B located ata first offset 154A, 154B into the data strip update value 118A, 118B.The first identifying data 150A, 150B may be selected such that acomparison between the data strip update value 118A, 118B and apre-update data value 158A, 158B read from the data strip 110A resultsin an inequality at the first offset 154A, 154B, 154C.

The journal entry 142 may further comprise location information 162 tolocate second identifying data 163 within the data strip 110A, 110B at asecond offset 164 equal to the first offset 154A, 154B, 154C uponre-boot following an unexpected RAID sub-system reset. The locationinformation 162 may comprise a stripe identification value 165, a diskdrive identification value 166 associated with a disk drive 161containing the data strip 110A, and a logical block address 167.

The apparatus 100 may further include a recovery module 170 coupled tothe journaling module 138 to analyze the journal entry 142 upon re-bootfollowing the unexpected RAID sub-system reset. The unexpected reset mayoccur during the disk drive updates, and during the re-boot a singledisk drive may be detected as failed.

The apparatus 100 may also include a stripe reconstruction module 174coupled to the journaling module 170 to reconstruct one or more of thefirst parity strip 122, the second parity strip 130, and the data strip110A. Reconstruction operations may utilize a plurality of strips fromnon-failed disks in the stripe 114, the first identifying data 150A ofthe data strip update value 118A read from the journal entry 142, orboth.

In another embodiment, a system 180 may comprise one or more of theapparatus 100, including logic 102 and a sequencing module 106 toestablish an order of operations associated with disk drive updates. Theupdates may be made to a data strip 110A using a data strip update value118A, to a first parity strip 122 using a first parity strip updatevalue 126, and to a second parity strip 130 using a second parity stripupdate value 134, as previously described. In some embodiments of thesystem 180, the first parity strip 122 may comprise a Q strip and thefirst parity strip update value 126 may comprise a Q strip update value.In other system 180 embodiments, the second parity strip 130 maycomprise the Q strip and the second parity strip update value 134 maycomprise the Q strip update value.

The system 180 may also include a journaling module 138 and a recoverymodule 170, as previously described. In some embodiments of the system180, the recovery module 170 may be included in a basic input-outputsystem associated with a RAID sub-system.

The system 180 may further include one or more processor(s) 184 coupledto the journaling module 138 to provide the data strip update value118A, and a display 188 coupled to the processor(s) 184 to display thedata strip update value 118A. The display 188 may comprise a cathode raytube display or a solid-state display such as a liquid crystal display,a plasma display, or a light-emitting diode display, among others.

Any of the components previously described can be implemented in anumber of ways, including embodiments in software. Thus, the apparatus100; logic 102; sequencing module 106; data strip 110A, 110B; RAIDsub-system 112; stripe 114; update values 118A, 118B, 126, 134; paritystrips 122, 130; journaling module 138; journal entry 142; non-volatilestorage medium 146; identifying data 150A, 150B, 163; offsets 154A,154B, 154C, 164; pre-update data value 158A, 158B; disk drive 161;location information 162; identification values 165, 166; logical blockaddress 167; recovery module 170; stripe reconstruction module 174;system 180; processor(s) 184; and display 188 may all be characterizedas “modules” herein.

The modules may include hardware circuitry, single or multi-processorcircuits, memory circuits, software program modules and objects,firmware, and combinations thereof, as desired by the architect of theapparatus 100 and system 180 and as appropriate for particularimplementations of various embodiments. Thus, the modules may beincluded in a system operation simulation package such as a softwareelectrical signal simulation package, a power usage and distributionsimulation package, a capacitance-inductance simulation package, apower/heat dissipation simulation package, a signaltransmission-reception simulation package, or any combination ofsoftware and hardware used to simulate the operation of variouspotential embodiments. These simulations may be used to characterize ortest the embodiments, for example.

It should also be understood that the apparatus and systems of variousembodiments can be used in applications other than RAID disk sub-systemupdate and recovery operations. Thus, various embodiments of theinvention are not to be so limited. The illustrations of apparatus 100and system 180 are intended to provide a general understanding of thestructure of various embodiments, and they are not intended to serve asa complete description of all the elements and features of apparatus andsystems that might make use of the structures described herein.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, modems, single ormulti-processor modules, single or multiple embedded processors, dataswitches, and application-specific modules, including multilayer,multi-chip modules. Such apparatus and systems may further be includedas sub-components within a variety of electronic systems, such astelevisions, cellular telephones, personal computers, workstations,radios, video players, vehicles, and others. Some embodiments mayinclude a number of methods.

FIG. 2 is a flow diagram illustrating several methods according tovarious embodiments of the invention. One such method may includesequencing write operations and journaling a portion of write data in adual-parity RAID sub-system such that one or more parity strips in astripe are consistent with target stripe data during the writeoperations. Write operations and journaling may proceed such that theconsistency of the parity strips is determinant following an unexpectedRAID sub-system reset occurring during the write operations.Consequently, the parity strips and the target stripe data may berecoverable following a disk drive failure and a power failure occurringduring the write operations.

The method 211 may begin at block 223 with ordering operationsassociated with disk drive updates in a RAID sub-system. The operationsmay include updates to a data strip associated with a stripe using adata strip update value. The operations may also include updates to afirst parity strip associated with the stripe using a first parity stripupdate value and updates to a second parity strip associated with thestripe using a second parity strip update value. Ordering may proceedsuch that the update to the first parity strip is written before writingthe update to the data strip and the update to the second parity stripis written after writing the update to the data strip.

The method 211 may also include reading a pre-update value from the datastrip, a pre-update value from the first parity strip, and a pre-updatevalue from the second parity strip, at block 231. The pre-update valuefrom the data strip may be read before creating a journal entry.

The method 211 may further include creating the journal entry in anon-volatile storage medium before writing the update to the firstparity strip, at block 237. The journal entry may comprise firstidentifying data within the data strip update value located at a firstoffset into the data strip update value. The first identifying data maybe selected such that a comparison between the data strip update valueand the pre-update data value read from the data strip results in aninequality at the first offset.

The journal entry may further comprise location information to locatesecond identifying data within the data strip at a second offset equalto the first offset upon re-boot following an unexpected RAID sub-systemreset. The location information may comprise one or more of a stripeidentification value, a disk drive identification value associated witha disk drive containing the data strip, and a logical block address. Thefirst offset and the second offset may comprise byte counts.

The method 211 may proceed at block 241 with calculating the firstparity strip update value using the pre-update value from the firstparity strip, the pre-update value from the data strip, and the datastrip update value. The first parity strip update value may becalculated after reading the pre-update value from the first paritystrip and before writing the first parity strip update value. The method211 may continue at block 245 with calculating the second parity stripupdate value using the pre-update value from the second parity strip,the pre-update value from the data strip, and the data strip updatevalue. The second parity strip update value may be calculated afterreading the pre-update value from the second parity strip and beforewriting the second parity strip update value.

The method 211 may also include writing the first parity strip updatevalue to the first parity strip after calculating the first parity stripupdate value and before writing the data strip update value, at block247. The method 211 may further include writing the data strip updatevalue to the data strip after writing the first parity strip updatevalue to the first parity strip and before writing the second paritystrip update value to the second parity strip, at block 251. The method211 may proceed at block 255 with writing the second parity strip updatevalue to the second parity strip after writing the data strip updatevalue to the data strip, and may continue at block 257 with clearing thejournal entry, perhaps after writing the second parity strip updatevalue.

The method 211 may also include analyzing journal entries if anunexpected RAID sub-system reset occurs during disk drive updateoperations and possibly if during a re-boot following the reset a singledisk drive is detected as failed, at block 261. The unexpected resetcondition may be tested for during RAID sub-system boot operations orsubsequently at block 259, wherein the existence of journal entries mayindicate that the unexpected reset has occurred. The method 211 mayinclude reading the first identifying data from the journal entry, atblock 265. The method 211 may also include reading the locationinformation from the journal entry to locate the second identifying datawithin the data strip, at block 269. The method 211 may further includereading the second identifying data from the data strip, at block 273.

The method 211 may continue at block 277 with comparing the firstidentifying data to the second identifying data. The method 211 mayinclude reconstructing the first parity strip using strips fromnon-failed disks in the stripe if the first identifying data is notequal to the second identifying data, at block 281. The method 211 mayalso include reconstructing the second parity strip using strips fromnon-failed disks in the stripe if the first identifying data is equal tothe second identifying data, at block 283. The method 211 may proceed atblock 287 with reconstructing the data strip using strips fromnon-failed disks in the stripe if the second identifying data cannot beread from the data strip. The method 211 may continue at block 290 withclearing the journal entry following the analysis of the journal entryand any data or parity strip reconstruction necessitated thereby. Themethod 211 may continue further with an analysis of additional journalentries and associated strip reconstruction activities at blocks261-290, for as long as the additional journal entries remain. Themethod 211 may conclude at block 293 when no additional journal entriesremain.

Some versions of the method 211 may describe operations associated witha RAID-6 sub-system. Operations may be ordered such that first parity isjournaled and written before second parity, as described above.Alternatively, operations may be ordered such that second parity isjournaled and written first. Thus, the second parity strip may comprisea Q strip, the pre-update value from the second parity strip maycomprise a pre-update value read from the Q strip, and the second paritystrip update value may comprise a Q strip update value. Alternatively,the first parity strip may comprise a Q strip, the pre-update value fromthe first parity strip may comprise a pre-update value read from the Qstrip, and the first parity strip update value may comprise a Q stripupdate value.

It may be possible to execute the activities described herein in anorder other than the order described. And, various activities describedwith respect to the methods identified herein can be executed inrepetitive, serial, or parallel fashion. Information includingparameters, commands, operands, and other data can be sent and receivedin the form of one or more carrier waves.

One of ordinary skill in the art will understand the manner in which asoftware program can be launched from a computer-readable medium in acomputer-based system to execute the functions defined in the softwareprogram. Various programming languages that may be employed to createone or more software programs designed to implement and perform themethods disclosed herein. The programs may be structured in anobject-orientated format using an object-oriented language such as Javaor C++. Alternatively, the programs can be structured in aprocedure-orientated format using a procedural language, such asassembly or C. The software components may communicate using a number ofmechanisms well known to those skilled in the art, such as applicationprogram interfaces or inter-process communication techniques, includingremote procedure calls. The teachings of various embodiments are notlimited to any particular programming language or environment. Thus,other embodiments may be realized, as discussed regarding FIG. 3 below.

FIG. 3 is a block diagram of an article 385 according to variousembodiments of the invention. Examples of such embodiments may comprisea computer, a memory system, a magnetic or optical disk, some otherstorage device, or any type of electronic device or system. The article385 may include one or more processor(s) 387 coupled to amachine-accessible medium such as a memory 389 (e.g., a memory includingelectrical, optical, or electromagnetic elements). The medium maycontain associated information 391 (e.g., computer program instructions,data, or both) which, when accessed, results in a machine (e.g., theprocessor(s) 387) sequencing write operations in a dual-parity RAIDsub-system, journaling a portion of write data, determining aconsistency of one or more parity strips following an unexpected RAIDsub-system reset occurring during the write operations, and recoveringfrom the unexpected reset, as previously described.

Implementing the apparatus, systems, and methods disclosed herein mayoperate to order and to journal RAID sub-system disk write operations toenable recovery from a power failure and a single disk drive failureoccurring while the write operations are in progress.

The accompanying drawings that form a part hereof show, by way ofillustration and not of limitation, specific embodiments in which thesubject matter may be practiced. The embodiments illustrated aredescribed in sufficient detail to enable those skilled in the art topractice the teachings disclosed herein. Other embodiments may beutilized and derived therefrom, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. This Detailed Description, therefore, is not to betaken in a limiting sense, and the scope of various embodiments isdefined only by the appended claims, along with the full range ofequivalents to which such claims are entitled.

Such embodiments of the inventive subject matter may be referred toherein individually or collectively by the term “invention” merely forconvenience and without intending to voluntarily limit the scope of thisapplication to any single invention or inventive concept, if more thanone is in fact disclosed. Thus, although specific embodiments have beenillustrated and described herein, any arrangement calculated to achievethe same purpose may be substituted for the specific embodiments shown.This disclosure is intended to cover any and all adaptations orvariations of various embodiments. Combinations of the aboveembodiments, and other embodiments not specifically described herein,will be apparent to those of skill in the art upon reviewing the abovedescription.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted to require morefeatures than are expressly recited in each claim. Rather, inventivesubject matter may be found in less than all features of a singledisclosed embodiment. Thus the following claims are hereby incorporatedinto the Detailed Description, with each claim standing on its own as aseparate embodiment.

1. An apparatus, including: logic in a dual-parity redundant array ofinexpensive disks (RAID) sub-system capable of sequencing writeoperations in the RAID sub-system and journaling a portion of write datasuch that at least one parity strip in a target stripe is consistentwith target stripe data during the write operations, such that theconsistency of each one of the at least one parity strip is determinantfollowing an unexpected RAID sub-system reset occurring during the writeoperations, and such that the at least one parity strip and the targetstripe data are recoverable following a disk drive failure and a powerfailure occurring during the write operations.
 2. The apparatus of claim1, further including: a sequencing module to establish an order ofoperations associated with disk drive updates to a data strip associatedwith the stripe using a data strip update value, to a first parity stripassociated with the stripe using a first parity strip update value, andto a second parity strip associated with the stripe using a secondparity strip update value in the RAID sub-system such that the update tothe first parity strip is written before writing the update to the datastrip and the update to the second parity strip is written after writingthe update to the data strip; and a journaling module coupled to thesequencing module to create a journal entry in a non-volatile storagemedium before writing the update to the first parity strip, wherein thejournal entry comprises first identifying data within the data stripupdate value located at a first offset into the data strip update value,the first identifying data selected such that a comparison between thedata strip update value and a pre-update data value read from the datastrip results in an inequality at the first offset, and wherein thejournal entry further comprises location information to locate secondidentifying data within the data strip at a second offset equal to thefirst offset upon re-boot following the unexpected RAID sub-systemreset.
 3. The apparatus of claim 2, further including: a recovery modulecoupled to the journaling module to analyze the journal entry uponre-boot following the unexpected RAID sub-system reset, wherein theunexpected reset occurs during the disk drive updates, and whereinduring the re-boot a single disk drive is detected as failed.
 4. Theapparatus of claim 2, further including: a stripe reconstruction modulecoupled to the journaling module to reconstruct at least one of thefirst parity strip, the second parity strip, and the data strip using atleast one of a plurality of strips from non-failed disks in the stripeand the first identifying data read from the journal entry.
 5. Theapparatus of claim 2, wherein the RAID sub-system comprises a RAID-6sub-system.
 6. The apparatus of claim 2, wherein the locationinformation further comprises: a stripe identification value; a diskdrive identification value associated with a disk drive containing thedata strip; and a logical block address.
 7. A system, including: logicin a dual-parity redundant array of inexpensive disks (RAID) sub-systemcapable of sequencing write operations in the RAID sub-system andjournaling a portion of write data such that at least one parity stripin a target stripe is consistent with target stripe data during thewrite operations, such that the consistency of each one of the at leastone parity strip is determinant following an unexpected RAID sub-systemreset occurring during the write operations, and such that the at leastone parity strip and the target stripe data are recoverable following adisk drive failure and a power failure occurring during the writeoperations; a processor coupled to the RAID sub-system to provide thewrite data; and a display coupled to the processor.
 8. The system ofclaim 7, further including: a sequencing module to establish an order ofoperations associated with disk drive updates to a data strip associatedwith a stripe using a data strip update value, to a first parity stripassociated with the stripe using a first parity strip update value, andto a second parity strip associated with the stripe using a secondparity strip update value in the RAID sub-system such that the update tothe first parity strip is written before writing the update to the datastrip and the update to the second parity strip is written after writingthe update to the data strip; and a journaling module coupled to thesequencing module to create a journal entry in a non-volatile storagemedium before writing the update to the first parity strip, wherein thejournal entry comprises first identifying data within the data stripupdate value located at a first offset into the data strip update value,the first identifying data selected such that a comparison between thedata strip update value and a pre-update data value read from the datastrip results in an inequality at the first offset, and wherein thejournal entry further comprises location information to locate secondidentifying data within the data strip at a second offset equal to thefirst offset upon re-boot following the unexpected RAID sub-systemreset.
 9. The system of claim 8, further including: a recovery modulecoupled to the journaling module to analyze the journal entry uponre-boot following the unexpected RAID sub-system reset, wherein theunexpected reset occurs during the disk drive updates, and whereinduring the re-boot a single disk drive is detected as failed.
 10. Amethod, including: sequencing write operations and journaling a portionof write data in a dual-parity redundant array of inexpensive disks(RAID) sub-system such that at least one parity strip in a stripe isconsistent with target stripe data during the write operations, suchthat the consistency of each one of the at least one parity strip isdeterminant following an unexpected RAID sub-system reset occurringduring the write operations, and such that the at least one parity stripand the target stripe data are recoverable following a disk drivefailure and a power failure occurring during the write operations. 11.The method of claim 10, further including: ordering operationsassociated with disk drive updates to (a) a data strip associated with astripe using a data strip update value, (b) a first parity stripassociated with the stripe using a first parity strip update value, and(c) a second parity strip associated with the stripe using a secondparity strip update value in the RAID sub-system such that the update tothe first parity strip is written before writing the update to the datastrip and the update to the second parity strip is written after writingthe update to the data strip; and creating a journal entry in anon-volatile storage medium before writing the update to the firstparity strip, wherein the journal entry comprises first identifying datawithin the data strip update value located at a first offset into thedata strip update value, the first identifying data selected such that acomparison between the data strip update value and a pre-update datavalue read from the data strip results in an inequality at the firstoffset, and wherein the journal entry further comprises locationinformation to locate second identifying data within the data strip at asecond offset equal to the first offset upon re-boot following theunexpected RAID sub-system reset.
 12. The method of claim 11, whereinthe first offset and the second offset comprise byte counts.
 13. Themethod of claim 11, wherein the location information further comprises:a stripe identification value; a disk drive identification valueassociated with a disk drive containing the data strip; and a logicalblock address.
 14. The method of claim 11, further including: readingthe pre-update value from the data strip, a pre-update value from thefirst parity strip, and a pre-update value from the second parity strip,wherein the pre-update value from the data strip is read before creatingthe journal entry.
 15. The method of claim 14, further including:calculating the first parity strip update value using the pre-updatevalue from the first parity strip, the pre-update value from the datastrip, and the data strip update value after reading the pre-updatevalue from the first parity strip and before writing the first paritystrip update value; and calculating the second parity strip update valueusing the pre-update value from the second parity strip, the pre-updatevalue from the data strip, and the data strip update value after readingthe pre-update value from the second parity strip and before writing thesecond parity strip update value.
 16. The method of claim 15, furtherincluding: writing the first parity strip update value to the firstparity strip after calculating the first parity strip update value andbefore writing the data strip update value; writing the data stripupdate value to the data strip after writing the first parity stripupdate value to the first parity strip and before writing the secondparity strip update value; writing the second parity strip update valueto the second parity strip after writing the data strip update value;and clearing the journal entry after writing the second parity stripupdate value.
 17. The method of claim 16, further including: analyzingthe journal entry upon re-boot following the unexpected RAID sub-systemreset, wherein the unexpected reset occurs during the disk driveupdates, and wherein during the re-boot a single disk drive is detectedas failed.
 18. The method of claim 17, further including: reading thefirst identifying data from the journal entry; reading the locationinformation from the journal entry to locate the second identifying datawithin the data strip; and reading the second identifying data from thedata strip.
 19. The method of claim 18, further including: comparing thefirst identifying data to the second identifying data.
 20. The method ofclaim 19, further including: reconstructing the first parity strip usingstrips from non-failed disks in the stripe if the first identifying datais not equal to the second identifying data; reconstructing the secondparity strip using strips from non-failed disks in the stripe if thefirst identifying data is equal to the second identifying data; andreconstructing the data strip using strips from non-failed disks in thestripe if the second identifying data cannot be read from the datastrip.
 21. The method of claim 20, wherein the second parity stripcomprises a Q strip, the pre-update value from the second parity stripcomprises a pre-update value read from the Q strip, and the secondparity strip update value comprises a Q strip update value.
 22. Themethod of claim 20, wherein the first parity strip comprises a Q strip,the pre-update value from the first parity strip comprises a pre-updatevalue read from the Q strip, and the first parity strip update valuecomprises a Q strip update value.
 23. An article including amachine-accessible medium having associated information, wherein theinformation, when accessed, results in a machine performing: sequencingwrite operations and journaling a portion of write data in a dual-parityredundant array of inexpensive disks (RAID) sub-system such that atleast one parity strip in a stripe is consistent with target stripe dataduring the write operations, such that the consistency of each one ofthe at least one parity strip is determinant following an unexpectedRAID sub-system reset occurring during the write operations, and suchthat the at least one parity strip and the target stripe data arerecoverable following a disk drive failure and a power failure occurringduring the write operations.
 24. The article of claim 23, wherein theinformation, when accessed, results in a machine performing: orderingoperations associated with disk drive updates to (a) a data stripassociated with a stripe using a data strip update value, (b) a firstparity strip associated with the stripe using a first parity stripupdate value, and (c) a second parity strip associated with the stripeusing a second parity strip update value in the RAID sub-system suchthat the update to the first parity strip is written before writing theupdate to the data strip and the update to the second parity strip iswritten after writing the update to the data strip; and creating ajournal entry in a non-volatile storage medium before writing the updateto the first parity strip, wherein the journal entry comprises firstidentifying data within the data strip update value located at a firstoffset into the data strip update value, the first identifying dataselected such that a comparison between the data strip update value anda pre-update data value read from the data strip results in aninequality at the first offset, and wherein the journal entry furthercomprises location information to locate second identifying data withinthe data strip at a second offset equal to the first offset upon re-bootfollowing the unexpected RAID sub-system reset.
 25. The article of claim24, wherein the information, when accessed, results in a machineperforming: analyzing the journal entry upon re-boot following theunexpected RAID sub-system reset, wherein the unexpected reset occursduring the disk drive updates, and wherein during the re-boot a singledisk drive is detected as failed.
 26. The article of claim 25, whereinthe information, when accessed, results in a machine performing: readingthe first identifying data from the journal entry; reading the locationinformation from the journal entry to locate the second identifying datawithin the data strip; and reading the second identifying data from thedata strip.
 27. The article of claim 26, wherein the information, whenaccessed, results in a machine performing: comparing the firstidentifying data to the second identifying data.
 28. The article ofclaim 27, wherein the information, when accessed, results in a machineperforming: reconstructing the first parity strip using strips fromnon-failed disks in the stripe if the first identifying data is notequal to the second identifying data; reconstructing the second paritystrip using strips from non-failed disks in the stripe if the firstidentifying data is equal to the second identifying data; andreconstructing the data strip using strips from non-failed disks in thestripe if the second identifying data cannot be read from the datastrip.
 29. The article of claim 28, wherein the second parity stripcomprises a Q strip, a pre-update value from the second parity stripcomprises a pre-update value read from the Q strip, and the secondparity strip update value comprises a Q strip update value.
 30. Thearticle of claim 28, wherein the first parity strip comprises a Q strip,a pre-update value from the first parity strip comprises a pre-updatevalue read from the Q strip, and the first parity strip update valuecomprises a Q strip update value.